Identification of an iridium-containing compound with a formal oxidation state of IX

Abstract

One of the most important classifications in chemistry and within the periodic table is the concept of formal oxidation states. The preparation and characterization of compounds containing elements with unusual oxidation states is of great interest to chemists. The highest experimentally known formal oxidation state of any chemical element is at present VIII, although higher oxidation states have been postulated. Compounds with oxidation state VIII include several xenon compounds (for example XeO4 and XeO3F2) and the well-characterized species RuO4 and OsO4 (refs 2-4). Iridium, which has nine valence electrons, is predicted to have the greatest chance of being oxidized beyond the VIII oxidation state. In recent matrix-isolation experiments, the IrO4 molecule was characterized as an isolated molecule in rare-gas matrices. The valence electron configuration of iridium in IrO4 is 5d(1), with a formal oxidation state of VIII. Removal of the remaining d electron from IrO4 would lead to the iridium tetroxide cation ([IrO4](+)), which was recently predicted to be stable and in which iridium is in a formal oxidation state of IX. There has been some speculation about the formation of [IrO4](+) species, but these experimental observations have not been structurally confirmed. Here we report the formation of [IrO4](+) and its identification by infrared photodissociation spectroscopy. Quantum-chemical calculations were carried out at the highest level of theory that is available today, and predict that the iridium tetroxide cation, with a Td-symmetrical structure and a d(0) electron configuration, is the most stable of all possible [IrO4](+) isomers.

Remarkably High Stability of Late Actinide Dioxide Cations: Extending Chemistry to Pentavalent Berkelium and Californium

“…Similarly,n either "praseodymyl(V)" nor Ir IX are likely to be stable in condensed phase;s ubstantial effort wasm ade to produce the latter but to no avail. [7] The AnO 2 + oxidation states assigned here are showni nT able 4a long with the known (and proposed)actinideoxidationstates. [25][26][27][28][29][30][31] Naturalpopulation analysis (NPA)…”

“…The recent discoveries of Pr V in PrO 2 + [4] and Ir IX in IrO 4 + [7] illustrate the ability to create new high oxidation states in isolated gas-phase molecules, particularly in oxide cations. Intrinsically stable high oxidation states can occur in isolated gasphase molecules because reduction of chemically fragile species by solvents or other interacting moieties is avoided.…”

Experimental and Theoretical Investigations of the Existence of CuII, CuIII, and CuIV in Copper Corrolato Complexes

“…[17] Thec yclic voltammograms and the differential pulse voltammograms of complexes 1, 2,a nd 3 were measured in CH 2 Cl 2 /0.1m TBAP (see Figure S1 and Table S2). Each of the three copper complexes displayed one reversible oxidation and one reversible reduction step.T he oxidation couple was (2), and À0.64(90) (3)v ersus ferrocene/ferrocenium. In the series 1!2!3,t he electronic effects of various substituents on the aryl rings on their redox potential visibly appeared to be insignificant.…”

“…[2] One reason for this quest is the involvement of metal centers in high oxidation states in various catalytic processes, [1b, 2] with the water oxidation reaction being ap rominent current example. [3] Them ost frequently encountered oxidation states of copper are 0 (usually in the metallic form) and + Ia nd + II in metal complexes and salts.…”

The Formal Oxidation States of Iridium Now Run from −III to +IX

“…For instance, the element E117 was reported quite recently [3] after E118, while compounds in the previously highest established oxidation state, + VIII, such as OsO 4 and XeO 4 have been known for decades. Examples of elements in the next positive oxidation state of + IX had remained elusive until the very recent report by Wang et al [1] On the anionic side, of interest for the present discussion, a series of formally 5d 10 6s 2 systems is known. In addition to cesium auride, CsAu, the bulk Cs 2 Pt was reported by the group of Jansen.…”